1. Field of the Invention
The present invention relates to a vacuum package, a method for manufacturing the vacuum package, a piezoelectric vibrator, and an oscillator, an electronic device, and a radio-controlled timepiece each having the piezoelectric vibrator.
2. Description of the Related Art
Recently, a piezoelectric vibrator (vacuum package) utilizing quartz or the like has been used in cellular phones and portable information terminals as the time source, the timing source of a control signal, a reference signal source, and the like. Although there are various piezoelectric vibrators of this type, a surface mounted device-type piezoelectric vibrator is known as one example thereof (for example, see JP-A-2002-124845).
As shown in FIGS. 18 and 19, a piezoelectric vibrator 200 includes a base substrate 201 and a lid substrate 202 which are anodically bonded to each other by a bonding film 207 and a piezoelectric vibrating reed 203 which is sealed in a cavity C formed between the two substrates 201 and 202.
The base substrate 201 and the lid substrate 202 are insulating substrates made of glass and the like. A penetration hole 204 is formed on the base substrate 201 so as to penetrate through the base substrate 201. A penetration electrode 205 is formed in the penetration hole 204 so as to block the penetration hole 204. The penetration electrode 205 is electrically connected to outer electrodes 206 which are formed on the outer surface of the base substrate 201 and is electrically connected to the piezoelectric vibrating reed 203 through lead-out electrodes 209 which are formed on the inner surface (inside the cavity C). The piezoelectric vibrating reed 203 is a tuning-fork type vibrating reed, for example, and is mounted on the lead-out electrodes 209 on the base end side thereof by a conductive adhesive E or the like. As shown in FIG. 19, the piezoelectric vibrator 200 is mounted when the outer electrodes 206 are connected to lands 211 provided on a silicon device 210 by a solder 212 or the like.
Subsequently, a method for manufacturing the piezoelectric vibrator described above will be described briefly based on FIG. 20. In FIG. 20, for better understanding of the drawings, the illustration of the piezoelectric vibrating reed 203 accommodated in the cavity C is omitted.
As shown in FIG. 20, a lid substrate wafer 220 in which a plurality of recess portions 220a for the cavity C is formed and a base substrate wafer 230 in which a plurality of piezoelectric vibrating reeds 203 (see FIG. 18) is mounted are anodically bonded by the bonding film 207 under a vacuum atmosphere. In this way, a wafer assembly 240 in which a plurality of piezoelectric vibrators 200 is formed in the matrix direction of the two wafers 220 and 230 is obtained. Thereafter, the wafer assembly 240 is cut in the matrix direction for each cavity C, whereby the wafer assembly 240 is fragmented into a plurality of piezoelectric vibrators 200.
However, in the step of manufacturing the piezoelectric vibrator 200, when the lid substrate wafer 220 and the base substrate wafer 230 are anodically bonded, outgas (for example, oxygen) is discharged from a bonding portion. At that time, the outgas is discharged from the outer circumferential ends of the two wafers 220 and 230 to the outside through the gap between the two wafers 220 and 230.
However, as described above, since the outer circumferential ends of the two wafers 220 and 230 serve as the discharge ports of the outgas discharged into the recess portions 220a, it is difficult to degas the outgas from the respective recess portions 220a. Therefore, there is concern that the two wafers 220 and 230 are anodically bonded in a state in which the outgas remains in the recess portion 220a. As a result, the degree of vacuum in the cavity C decreases, and an equivalent resistance value (effective resistance value: Re) increases. In this case, there is a problem in that the driving voltage of the piezoelectric vibrator 200 increases, and thus energy efficiency decreases.
Furthermore, when the piezoelectric vibrator 200 is mounted on the silicon device 210, since the outer electrodes 206 and the lands 211 are surface-to-surface bonded, there is a problem in that it is difficult to form fillets (the wet portions of the solder 212 flowing over the side surfaces of the piezoelectric vibrator 200 to cover the side surfaces) to the side surfaces of the piezoelectric vibrator 20, and a mounting strength is low.